I agree with the above. The sawdust bucket is great for a family or small group of committed people. The small self-contained commercial composting toilets that you could install in 2nd floor bathrooms have never looked like a good choice to me, for various reasons including what Dave mentioned above. I think composting needs
enough space so that you can leave the contents there for enough time, eg one year...
I have heard a lot about
urine diverting toilets and share house with a passionate believer in the concept (though our current toilet is all mixed). But from what I've read and the few units I've seen, it seems to me like a urine separating seat is again, only good for a committed small group of users, not for a changing clientele of B&B guests. I've heard that first time users and small children might foul the urine part of a urine separating seat.
For a B&B, you need something that looks as much like a standard toilet seat in the bathroom as possible, and that has a "remote chamber" ie a large composting chamber directly below, with a wide enough chute not to get fouled.
Active electric ventilation doesn't use a lot of power, and is very helpful for preventing events that would alarm guests, like any fly or smell problem. It keeps the pile dryish, and keeps the air moving from the bathroom, through the toilet and out o the building, never the other way into the room.